Serum lipids, lipoproteins, apolipoproteins and paraoxanase enzyme activity in patients with thyroid dysfunction

Lipid and lipoprotein metabolism is affected by many factors, among them thyroid hormones. Lipid and apolipoprotein disorders are common findings in patients with thyroid dysfunction. Moreover, LDL-C oxidation is more common in these patients than the normal population. This study aims at assessing lipids, lipoproteins, apolipoproteins and serum paraoxonase activity in patients with thyroid dysfunction and comparing them with normal controls. In this study 99 patients with thyroid dysfunction (49 hypothyroid and 50 hyperthyroid) were each compared with a separately age and sex matched control group of 50. A fasting blood sample was obtained and serum total cholesterol, triglycerides, apolipoproteins A-I and B, and paraoxonase activity were measured. In hyperthyroid patients, significant reductions in serum paraoxonase activity (45±23 vs. 67±37 Iu/ml, P<0.001), triglycerides (112±53 vs. 166±130 mg/dl, P<0.05), apolipoprotein A-I (137±26 vs. 154±21 mg/dl, P<0.001) and apolipoprotein B (75±18 vs. 85±25 mg/dl, P<0.05) were found. Hypothyroid patients had lower paraoxonase activity (46±21 vs. 64±32 Iu/ml, P<0.005) than controls and higher total cholesterol (224±69 vs. 185±41 mg/dl, P<0.001), LDL-C (133±59 vs. 93±36 mg/dl, P<0.001), and apo B (107±37 vs. 84±23 mg/dl, P<0.001). The results show significant changes of lipid levels in thyroid dysfunction, like previous studies. Also, for the first time in both hypo and hyperthyroid patients we observed significant reduction in serum paraoxonase activity. According to these findings, increased LDL oxidation in thyroid dysfunction, at least to some extent, can be attributed to reduced serum paraoxonase activity.